The present invention relates to testing of radio frequency (RF) wireless signal transceivers, and in particular, to testing such devices without a need for RF signal cables for conveyance of RF test signals.
Many of today's electronic devices use wireless technologies for both connectivity and communications purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential of interfering with the operations of one another by virtue of their signal frequencies and power spectral densities, these devices and their wireless technologies must adhere to various wireless technology standard specifications.
When designing such devices, engineers take extraordinary care to ensure that such devices will meet or exceed each of their included wireless technology prescribed standard-based specifications. Furthermore, when these devices are later being manufactured in quantity, they are tested to ensure that manufacturing defects will not cause improper operation, including their adherence to the included wireless technology standard-based specifications.
For testing these devices following their manufacture and assembly, current wireless device test systems (“testers”) employ a subsystem for analyzing signals received from each device. Such subsystems typically include at least a vector signal generator (VSG) for providing the source signals to be transmitted to the device, and a vector signal analyzer (VSA) for analyzing signals produced by the device. The production of test signals by the VSG and signal analyses performed by the VSA are generally programmable so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless technology standards with differing frequency ranges, bandwidths and signal modulation characteristics.
Calibration and performance verification testing of a device under test (DUT) are typically done using electrically conductive signal paths, such as RF cables, rather than wireless signal paths, by which a DUT and tester communicate via electromagnetic radiation. Accordingly, the signals between the tester and DUT are conveyed via the conductive signal path rather than being radiated through ambient space. Using such conductive signal paths helps to ensure repeatability and consistency of measurements, and eliminates positioning and orientation of the DUT as a factor in signal conveyance (transmission and reception).
In the case of a multiple input, multiple output (MIMO) DUT, a signal path must be provided, in some form, for each input/output connection of the DUT. For example, for a MIMO device intended to operate with three antennas, three conductive signal paths, e.g., cables and connections, must be provided for testing.
However, using conductive signal paths significantly impacts the time needed for testing each DUT due to the need for physically connecting and disconnecting the cables between the DUT and tester. Further, in the case of a MIMO DUT, multiple such connecting and disconnecting actions must be performed, both at the beginning and termination of testing. Further, since the signals being conveyed during testing are not radiated via the ambient space, as they would be in the normally intended use, and the antenna assemblies for the DUT are not in use during such testing, such testing does not simulate real world operation and any performance characteristics attributable to the antennas are not reflected in the test results.
As an alternative, testing could be done using test signals conveyed via electromagnetic radiation rather than electrical conduction via cables. This would have the benefit of requiring no connecting and disconnecting of test cables, thereby reducing the test time associated with such connections and disconnections. However, the “channel” in which the radiated signals and receiver antennas exist, i.e., the ambient space through which the test signals are radiated and received, is inherently prone to signal interference and errors due to other electromagnetic signals originating elsewhere and permeating the ambient space. Such signals will be received by the DUT antennas and can include multipath signals from each interfering signal source due to signal reflections. Accordingly, the “condition” of the “channel” will typically be poor compared to using individual conductive signal paths, e.g., cables, for each antenna connection.
One way to prevent, or at least significantly reduce, interference from such extraneous signals, is to isolate the radiated signal interface for the DUT and tester using a shielded enclosure. However, such enclosures have typically not produced comparable measurement accuracy and repeatability. This is particularly true for enclosures that are smaller than the smallest anechoic chambers. Additionally, such enclosures tend to be sensitive to the positioning and orientation of the DUT, as well as to constructive and destructive interference of multipath signals produced within such enclosures.
Accordingly, it would be desirable to have systems and methods for testing wireless signal transceivers, and particularly wireless MIMO signal transceivers, in which radiated electromagnetic test signals can be used, thereby simulating real world system operation as well as avoiding test time otherwise necessary for connecting and disconnecting test cabling, while maintaining test repeatability and accuracy by avoiding interfering signals due to externally generated signals and multipath signal effects.